Analyzing Earth History
Data
Student Activity Pages
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Name ____________________________Date _____________Period_____
Understanding Mass Extinctions:
Graphing Diversity Data
Student Version
Part One: Understanding Mass Extinctions
Objective:
We are going to look at diversity of specific genera to see what patterns we see over
time and develop our understanding of how scientists determine when mass
extinctions occur by using data from the fossil record. Genera is plural for genus. All
life is organized into kingdom, phylum, class, order, family, genus, species. Kingdom
being the most broad while species is the most specific. We will investigate three
coral building organisms and see how their diversity has changed throughout
geologic time. Through our analysis of this limited set of data we see trends. This
gives us a basis for understanding how scientists take data from thousands of fossils
and draw conclusions about mass extinction events.
Background Information:
Mass extinctions have sometimes accelerated the evolution of life on Earth.2 When
dominance of particular ecological niches passes from one group of organisms to
another, it is rarely because the new dominant group is "superior" to the old and
usually because an extinction event eliminates the old dominant group and makes
way for the new one. For example mammaliformes ("almost mammals") and then
mammals existed throughout the reign of the dinosaurs, but could not compete for
the large terrestrial vertebrate niches, which dinosaurs monopolized. The endCretaceous mass extinction removed the non-avian dinosaurs and made it possible
for mammals to expand into the large terrestrial vertebrate niches. Ironically, the
dinosaurs themselves had been beneficiaries of a previous mass extinction, the endTriassic, which eliminated most of their chief rivals, the crurotarsans.
Another point of view put forward in the Escalation hypothesis predicts that species
in ecological niches with more organism-to-organism conflict will be less likely to
survive extinctions. This is because the very traits that keep a species numerous and
viable under fairly static conditions become a burden once population levels fall
among competing organisms during the dynamics of an extinction event. One
prediction of the Escalation Hypothesis is that individual species having fewer
adaptations that enable them to compete with other life forms are more likely to
survive a mass extinction event such as one of The Big Five. This is because there is
more flexibility to fit into new ecological niches that arduous adaptations such as
heavy shells or energy consuming venom production would hinder.
Furthermore, many groups, which survive mass extinctions do not recover in
numbers or diversity, and many of these go into long-term decline, and these are
often referred to as "Dead Clades Walking". So analyzing extinctions in terms of
"what died and what survived" often fails to tell the full story.
2
http://en.wikipedia.org/wiki/Extinction_event
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PreLab Questions:
1. Historically mass extinctions have allowed certain species to fill the niches of
extinct species. Scientist propose that the species filling the niches of the
extinct species are not dominant in anyway but rather utilizing resources
made available through the extinction of a species. What species have
benefited from the extinction of other species?
2. Why would it be a disadvantage of a mass extinction survivor species to be
extremely adapted to a certain environment?
3. At a mass extinction event, do all species go extinct immediately or do some
species gradually die out? Explain your answer.
Procedure: Graphing Diversity Data
Your objective is to graph the diversity data from the Paleobiology database. The
Paleobiology database is a collection of data relating to the fossil record obtained
from the research of hundreds of scientists.
Take the data from the attached data tables and create a graph with all organisms on
one graph. The Paleobiology database provides a lot of information about the fossil
record but we will only graph the range through genera column, which refers to the
number of genera present in that division of time. Additionally, we will graph the
interval, which refers to the time period. Each time period is divided into equal
sections to give a more detailed despersion of diversity during that time period.
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Rugosa Data
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Tabulata Data
Archaeocyatha Data
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Diversity Curve Data Analysis
1. Looking at the graph, what do you notice happened to the diversity of these
genera at the end of the Ordovician?
2. What happens to the reef building genera at the end of the Devonian?
3. Was the decline of the Tabulata gradual or sudden?
4. How does the decline of Tabulata compare to the decline of Rugosa?
5. What trend do you notice when looking at the three different types of corals or
reef building organisms? When do they originate versus go extinct? Give a
general overview of what the fossil record looks like for corals represented in
this graph?
6. Why do we not find many fossils before the Cambrian?
Scientists take the data sets from these organisms and thousands of others. From
analyzing all of these data sets together scientists have determined when mass
extinctions have occurred. We have looked at a very narrow range of results in our
graph but if we expanded this to a very large range of organisms we will see some
more trends.
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Now we will look at the graph provided.
All Genera Through Time Graph
image from: http://en.wikipedia.org/wiki/Extinction_event
Analysis:
1. Following the trend line, what is the general trend of the graph? What is
happening to biodiversity over geologic time?
2. What are some reasons why scientists would observe an increase in diversity
of organisms throughout the history of the Earth?
3. Find the end of the Paleozoic (251 ma) and Mesozoic (65.5 ma) on the graph.
What do you notice happens to the graph? What does this indicate
happened?
4. How does diversity today compare to diversity at the early Cambrian?
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5. What guess do you have for why this graph starts at 542 million years and not
further back in Earth’s history?
Part Two: Sampling Inquiry
Evaluating what information we do have
Scientists who evaluate the fossil record and draw conclusions from it must be
mindful of the data that is present and the lack of certain data. The fossil record has
a relative abundance of certain organisms that are favorable to being preserved and
lacks the presence of other organisms that are more difficult to preserve. We know
organisms with a hard shell or calcium carbonate will preserve better and be more
numerous in the fossil record than soft bodied animals that has tissue that is easily
damaged by decay and environmental conditions surrounding where the organism
dies. Additionally, when scientists analyze data such as the diversity curve data that
we just graphed, scientists must be sure they have a large enough sample size that is
statistically significant or unlikely to have occurred by chance.
You already understand that you need a certain sample size to get a representative
sampling of a population. If I asked you to find out what the favorite ice cream flavor
of students in your class is you would not go out and ask two students in order to
draw your conclusion.
This activity helps us understand and experience how scientist must evaluate how
much data in a sample provides enough evidence to draw accurate conclusion.
Scientists refer to this as confidence intervals, which refer to how scientists use
statistics to confirm the conclusions they are making.
Objective: 3
Your goal is to collect a sample of data from your classmates regarding what sport is
the easiest to play. You have two minutes to sample your classmates to obtain your
data regarding your question.
Question:
Hypothesis:
Procedure: How will you sample the class to collect a representative amount of
data?
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Lesson adapted from Learning to take scientific samples: holey card activity presented by Miriam
Polne
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Data/Results:
Conclusion:
1. Do you feel you got an accurate sampling of the class? Explain why or why
not.
2. What would be the most accurate way to collect a 100% accurate sampling?
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Paleontologists and geologists do not have fossils from all organisms that have
ever existed. This is because some organisms have bodies that do not preserve
well, conditions for fossils to form are somewhat rare, environmental conditions
can make it difficult for organisms to be preserved, and fossils can be preserved
in rock that is weathered and destroyed during the rock cycle. Understanding
the factors that reduce the number of available fossils, scientists must be aware
of the numerous factors affecting sample sizes of fossils they do have.
Now take the four envelopes and make a hypothesis for what image is inside the
envelope. The same image is in each envelope. Each envelope represents a
different sample size.
Hypothesis Envelope #1
Hypothesis Envelope #2
Hypothesis Envelope #3
Hypothesis Envelope #4
Analysis:
1. Did your hypothesis change as you gathered more information?
2. Were all envelopes and their respective samples of equal value? Explain
why or why not. Were any of the samples (associated with an envelope)
misleading? Explain why or why not.
3. Was there a point at which you were confident that you had enough
information?
4. We will never have a fossil for each organism that has ever existed or
even created a fossil. How does this activity relate to our collections of
fossils in the fossil record?
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5. Are there other factors in addition to number of samples that would affect
the distribution or abundance of fossils created at a particular time in
history?
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Part Three: Taphonomy Lab
The field of taphonomy in paleontology was born out of a discovery in the 1950ʼs by
scientists named Knoll and Barghoorn. They looked at the decay of algae to see what
changes occurred to the algae over time.4 They discovered that the protoplasmic
(stuff inside a cell membrane) material decay in such a way that it looked like a
nucleus. This disproved many of the early images of eukaryotic cells that were found
in chert (rock like charcoal) prior to their discovery. While scientists have a lot of
confidence in their findings in the fossil record, this discovery challenged the early
evidence of eukaryotic cells. This study introduced the importance of a field called
taphonomy. Taphonomy studies the role of decay in changing an organism’s
appearance and how they become fossils. This has extended into our study of
forensics in a field called forensic taphonomy where we look at decay in human
bodies to help solve mysteries about a crime. The new discoveries by Knoll and
Barghoorn and the emerging field of taphonomy challenged scientist to reevaluate
the fossil record and potential biases it held. The goal of taphonomy is to see what
bias exists in the fossil record regarding the relative abundances of organisms. Since
we know organisms with a hard shell or calcium carbonate will preserve better and
be more numerous in the fossil record than soft bodied animals that has tissue that
is easily damaged by decay and environmental conditions surrounding where the
organism dies. Experimental taphonomy testing usually consists of exposing the
remains of organisms to various altering processes, and then examining the effects
of the exposure.5
Prelab Questions:
1. What is the study of taphonomy?
2. Why is it important that scientists understand taphonomy as it relates to the
fossil record?
Now we will conduct our own taphonomy study using paramecium. We are using
paramecium, a single celled eukaryotic cell, because they are large enough to see in
a compound light microscope and their long unique body shape makes them easy to
identify. We will compare the paramecium under normal circumstances and alter
the environmental conditions to see how it affects the rate of decay or appearance of
organism.
1. What will you do for your control experiment?
4
Precambrian Eukaryotic Organisms: A Reassessment of the Evidence. Andrew H. Knoll; Elso S.
Barghoor Science, New Series, Vol. 190, No. 4209. (Oct. 3, 1975), pp. 52-54.
5 http://en.wikipedia.org/wiki/Taphonomy
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2. What variable or environmental condition are you altering?
3. What environmental condition in the real world is this analogous to?
Complete the lab report form. Record what you plan to do for the experiment.
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The Current Mass Extinction
Is the biosphere today on the verge of anything like the mass extinctions of the
geological past?6 Could some equivalent of meteorite impacts or dramatic climate
change be underway, as humankind's rapid destruction of natural habitats forces
animals and plants out of existence?
Increasingly, researchers are doing the numbers, and saying, yes, if present trends
continue, a mass extinction is very likely underway. The evidence is pieced together
from details drawn from all over the world, but it adds up to a disturbing picture.
This time, unlike the past, it's not a chance asteroid collision, nor a chain of climatic
circumstances alone that's at fault. Instead, it is chiefly the activities of an evergrowing human population, in concert with long-term environmental change.
The background level of extinction known from the fossil record is about one
species per million species per year, or between 10 and 100 species per year
(counting all organisms such as insects, bacteria, and fungi, not just the large
vertebrates we are most familiar with). In contrast, estimates based on the rate at
which the area of tropical forests is being reduced, and their large numbers of
specialized species, are that we may now be losing 27,000 species per year to
extinction from those habitats alone.
The typical rate of extinction differs for different groups of organisms. Mammals, for
instance, have an average species "lifespan" from origination to extinction of about 1
million years, although some species persist for as long as 10 million years. There
are about 5,000 known mammalian species alive at present. Given the average
species lifespan for mammals, the background extinction rate for this group would
be approximately one species lost every 200 years. Of course, this is an average rate
-- the actual pattern of mammalian extinctions is likely to be somewhat uneven.
Some centuries might see more than one mammalian extinction, and conversely,
sometimes several centuries might pass without the loss of any mammal species. Yet
the past 400 years have seen 89 mammalian extinctions, almost 45 times the
predicted rate, and another 169 mammal species are listed as critically endangered.
Therein lies the concern biologists have for many of today's species. While the
number of actual documented extinctions may not seem that high, they know that
many more species are "living dead" -- populations so critically small that they have
little hope of survival. Other species are among the living dead because of their
interrelationships -- for example, the loss of a pollinator can doom the plant it
pollinates, and a prey species can take its predator with it into extinction. By some
estimates, as much as 30 percent of the world's animals and plants could be on a
path to extinction within 100 years. These losses are likely to be unevenly
distributed, as some geographic areas and some groups of organisms are more
6
http://www.pbs.org/wgbh/evolution/library/03/2/l_032_04.html
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vulnerable to extinction than others. Tropical rainforest species are at especially
high risk, as are top carnivores, species with small geographic ranges, and marine
reef species.
Humanity's main impact on the extinction rate is landscape modification, an impact
greatly increased by the burgeoning human population. Now standing at 5.7 billion
and growing at a rate of 1.6 percent per year, the population of the world will
double in 43 years if growth continues at this pace. By draining wetlands, plowing
prairies, logging forests, paving, and building, we are altering the landscape on an
unprecedented scale. Some organisms do well under the conditions we've created:
They tend to cope well with change, tolerate a broad range of habitats, disperse
widely, and reproduce rapidly, and they can quickly crowd out more specialized
local species. City pigeons, zebra mussels, rats, and kudzu and tamarisk trees -these are examples of what biologists call "weedy" species, both animals and plants.
Many weedy species will probably survive, and even thrive, in the face of the current
mass extinction. But thousands of others, many never known to science, are likely to
perish.
And what is the fate of our own species likely to be, if we really are in the midst of a
sixth mass extinction? One possibility is that as diversity and abundance wither, the
species causing it all -- Homo sapiens, the most dominant species in history -- could
also be on the road to oblivion. But another possibility is that Homo sapiens, which
has proved to be a very effective weedy species itself, will persist. That's the view of
paleobiologist David Jablonski, who sees us as one of the survivors, "sort of picking
through the rubble" of a world that has lost much of its biodiversity -- and much of
its comfort. For along with that species richness, the ecosystem is likely to loose
much of its ability to provide many of the valuable services that we take for granted,
from cleaning and recirculating air and water, to pollinating crops and providing a
source for new pharmaceuticals. And while the fossil record tells us that
biodiversity has always recovered, it also tells us that the recovery will be
unbearably slow in human terms -- 5 to 10 million years after the mass extinctions
of the past. That's more than 200,000 generations of humankind before levels of
biodiversity comparable to those we inherited might be restored.
Conclusion Questions:
1. How does the rate of extinction today compare to historically?
2. Why is it important to understand how the Earth has changed geologically and
biologically?
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3. The article says that while the number of actual documented extinctions may
no seem that high, they know that many more species are “living dead.” What
are the “living dead” that many biologists are concerned about?
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4. According to the article, what are humanity’s main impacts on the extinction
rate of species today?
5. What environmental challenges are happening to habitat in your local area.
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